1. Field of the Invention
This invention relates to tap cocks and stop valves and in particular to an auxiliary tap valve either for retrofit or built in incorporation into screw down acting taps and valves for controlling fluid or water flow by automatically shutting off the flow of water through a tap during maintenance and reducing operating water flow to assist in water conservation.
2. Description of the Related Art
A vast array of valves, cocks and taps exist for controlling the flow and delivery of liquids and gases.
Such devices vary from the simple plug cocks which provide a transverse plug to interrupt the flow of a gas or liquid in a supply line, where the plug is provided with a hole capable of rotational alignment with the input and output supply lines to effect control over the flow of gases and liquids, to complex sluice valves involving a number of components.
For the supply and control of water, in particular to domestic situations, a screw down stop valve is commonly incorporated into a tap cock such that a washer is made to bear down on an orifice through which water passes. Such devices fall midway between simple plug cocks and complex valves and find extensive application in the control of water supply.
The screw down stop valve provides a screw operated spindle as an activating means for the washer such that a high degree of control can be exercised over the washer and therefore over the flow of water through the orifice. Such screw down stop valves are commonly known as bib cocks and find wide application in domestic water control.
The bib cock provides a body through which water passes via an internal gate which is opened and closed by the screw action of a spindle urging a washer against the seat of an orifice in the gate to close off the water supply. However, if the washer fails or wears out, as they are bound to do, it is necessary to arrest the supply of water to the tap in question before the washer can be removed and replaced.
The requirement for shut down of a water supply prior to maintenance can often cause great inconvenience or danger to other users or systems fed from a common source. For example, in a block of flats or apartments it is often necessary to interrupt the water supply to the whole block in order to fix one tap. In a commercial situation, if a water tap requires maintenance it can be time consuming and often difficult to locate the site of a mains water control tap. In addition, industrial situations may require a constant supply of water or other liquids which cannot be interrupted until the end of a shift or run. If a tap is faulty in such a situation it may be impossible or very difficult to interrupt the mains supply in order to service the faulty tap.
A number of devices have been proposed to finction as intermediate valves in the above described situation.
For example, Australian Patent Application No. 59752/80 discloses a valve assembly to enable repair work to be performed without having to shut off the water supply. Similarly Australian Patent Application No. 70219/74 discloses an improved fluid valve involving a complex arrangement of valve members and springs adapted to close off the main water supply to a tap to facilitate maintenance.
The currently available devices operate in one of two ways;
a) either by a positive bias of the auxiliary valve in the form of a mechanical element like a spring which urges the valve closed; or,
b) by a passive action relying on the back pressure supplied by the fluid stream itself which actuates the valve and urges it into the closed position by following the direction of flow of the fluid.
The current devices which operate on either of the above systems suffer numerous serious drawbacks. The positively biased devices are totally dependent for their reliability on a spring which can fail and require major maintenance. Furthermore, such spring devices involve complicated manufacture and assembly and corresponding high costs as well as a limitation on the retrofittability of such mechanisms.
On the other hand passive devices that rely on the back pressure supplied by the flow of fluid in the direction from the fluid supply (upstream) through the top gate to the outlet (downstream) to close the valve also suffer problems; principally in the smooth and positive operation of the valve which can suffer if any turbulence is caused in the gate area of a tap. In particular, unless the valve is very specifically placed within the tap gate, the back pressure of the fluid may not be uniformly or positively applied to the underface or upstream face of the valve so as to push the valve closed, but may also be applied to the upper face of the valve and cause a counteracting force to keep the valve open. The resultant forces on the valve can cause excessive clatter and efficient operation.